Since their first commercialization in the 1990s, rechargeable lithium-ion (Li-ion) batteries have served as major power sources for a wide range of electronic products. An increase in global energy demand, rising and fluctuating crude oil prices, and environmental concerns in recent years have led to an increase in demand for Li-ion batteries. In particular, Li-ion battery technology is being developed for applications in electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). For such applications, improved Li-ion batteries providing high energy density and high power capacity are required.
In general, the energy density of a Li-ion cell depends on the cathode material used in the cell. Typically, lithium transition metal oxides are used as lithium-ion battery cathode materials. In general, the morphology of such lithiated metal oxides is dependant on the starting metal precursors and the synthetic methods employed. Both of these considerations also play an important role in controlling the electrochemical properties of the cathode materials in Li-ion cells.
The most common industrial method for preparation of materials for Li-ion batteries is the hydroxide co-precipitation method. In this method, transition metal sulfates in aqueous solutions are reacted with sodium hydroxide solution under very corrosive alkaline conditions to fabricate transition metal hydroxides. The transition metal hydroxides are used to synthesize the lithium transition oxide materials that are used as positive active materials in lithium ion cells. As an alternative, a carbonate co-precipitation method may be used. Such a method uses sodium carbonate to synthesize battery grade materials. The advantage of this method over the hydroxide method is the preservation of the oxidation states of transition metals in the +2 oxidation state in the prepared carbonate precursors. However, both the hydroxide and carbonate co-precipitation methods may result in contamination of the precursors during the formation of particles with contaminants such as sodium and sulfur which are used in the precipitation processes. These species cannot be avoided even after extensive washing because they are precipitated as sodium sulfate Na2SO4 during the co-precipitation of the transition metal hydroxides and carbonates. The presence of such impurities in the electrode materials negatively impacts the performance of the Li-ion cells.